NMEA Network

[MarkSF]

Originally Posted by CarinaPDX

Welcome to CF!

Agree that N2K is the way to go. Most multi-function displays (MFDs) support display of data off of the N2K bus. I like the way Furuno uses the standard DeviceNet connectors, but you can get adapter cables for Raymarine's SeaTalk NG and Simrad's Simnet connectors.

I was just at the Seattle Boat Show and saw an N2K-WiFi bridge that enabled an iPad to display the N2K data. Pretty cool. Personally I have an N2K to USB bridge but haven't yet found my ideal display of N2K on the computer.

N2K is not necessarily more expensive than the alternatives; the big issue is the cost of the MFD or computer or whatever is used to display the data. The sensors tend to be competitively priced. By having an MFD or similar then all of the sensors can be headless, which saves a lot of money. For instance, my depth sounder and knotmeter transducers have N2K DeviceNet cables coming out of them, ready to plug into the backbone; they were less expensive than stand-alone units that include their own displays. Masthead wind sensors, solid-state compasses, AIS receivers and transceivers are all available as sensors without displays.

Airmar is the giant in the marine sensor business; many of their products are sold through the big name instrument companies. They have some excellent N2K sensors (my knotmeter and depth sounder included). Maretron also makes N2K sensors (my solid state compass, wind sensor) and is the biggest player in cabling for N2K.

I have found Blue Heron to be a great place to find a wide assortment of N2K products at very competitive prices: Marine Technology | Blue Heron Marine Electronics . (My only relationship with them is as a customer.)

Did you have any trouble with accuracy of the NMEA2000 knotmeter? I have the Airmar DST800 (badged as Garmin) and it's over-reading about 20%. My Lowrance chartplotter is the display device and doesn't appear to have a calibrate function.

[CarinaPDX]

Since I am installing a new engine, and doing a whole lot of other things, I haven't been out to check the accuracy. However, it is not unusual for knotmeters to require calibration, and 20% is not extreme. Whatever you are using as a display should have a calibration facility: look in the setup menu. There is usually an ability to adjust by +/- %.

Good luck,

Greg

[CarinaPDX]

Just noticed you answered that. So what is the Lowrance model #? Do you have a manual? There is probably a pdf online.

Greg

[CarinaPDX]

Lowrance manuals available here if needed: Manuals

[MarkSF]

Originally Posted by CarinaPDX

Just noticed you answered that. So what is the Lowrance model #? Do you have a manual? There is probably a pdf online.

Greg

It is a Lowrance HDS-5M. I have the manual and it makes almost no mention of calibrating speed sensors. It just says that if you can calibrate an NMEA2000 device, the "calibrate" option will appear when you select it in Devices. When I select the DST800, the only adjustable option is depth offset.

[CarinaPDX]

That sounds like a mistake on their part. Have you upgraded to 4.0 software? If not, do it and try again. If so then get on to customer service and have them add this to their bug tracker so it will be fixed in a future release. If you need to go that way then cc: Airmar as they will want this fixed as well and may have some leverage.

Good luck. I'm off to bed.

Greg

Edit: Of course it is also possible that Airmar made a mistake, or that Garmin had proprietary firmware put into their brand of the unit which would not be understood by generic N2K controllers.

[s/v Jedi]

Originally Posted by CarinaPDX

That sounds like a mistake on their part. Have you upgraded to 4.0 software? If not, do it and try again. If so then get on to customer service and have them add this to their bug tracker so it will be fixed in a future release. If you need to go that way then cc: Airmar as they will want this fixed as well and may have some leverage.

Good luck. I'm off to bed.

Greg

Edit: Of course it is also possible that Airmar made a mistake, or that Garmin had proprietary firmware put into their brand of the unit which would not be understood by generic N2K controllers.

The only two vendors that I know of and will cooperate for these calibrations are Maretron and Airmar, i.e. you can calibrate an Airmar sensor from a Maretron display or their "free" N2KAnalyzer software (needs the USB100 interface).

Lowrance is still at the arrogant pov that you must buy their sensor, even when it's the same hardware.

ciao!
Nick.

[colemj]

I can calibrate our Airmar transducers using the Simrad autopilot control head. I'm pretty sure the Furuno MFD will also, but I will have to check that again.

Mark

[Ziggy]

Originally Posted by MarkSF

Did you have any trouble with accuracy of the NMEA2000 knotmeter? I have the Airmar DST800 (badged as Garmin) and it's over-reading about 20%. My Lowrance chartplotter is the display device and doesn't appear to have a calibrate function.

Garmin GMI-10 has a calibrate function that works with the Airmar N2K knot meter and uses GPS as reference. To get an accurate calibration you have to do it on a calm day (no wind) at slack tide (no current). The whole procedure is pretty straightforward but it takes a few minutes: it involves getting the boat to move under engine at a reasonable cruising speed and then slowing down to dead in the water.

[DotDun]

In a multi-vendor N2K network, one of the marketed features of N2K, how does one update the firmware on a sensor from vendor A with a display from vendor B??

I know that Garmin sensors require a Garmin display, Furuno sensors require a Furuno MFD, Raymarine sensors require a RM MFD. Airmar? Simrad? Others?

I'm won't tell anyone to stay away from N2K, but I will tell them, 'They'll be dragons in there!'. Be careful mixing and matching vendors.

[MarkSF]

Originally Posted by Ziggy

Garmin GMI-10 has a calibrate function that works with the Airmar N2K knot meter and uses GPS as reference. To get an accurate calibration you have to do it on a calm day (no wind) at slack tide (no current). The whole procedure is pretty straightforward but it takes a few minutes: it involves getting the boat to move under engine at a reasonable cruising speed and then slowing down to dead in the water.

Thanks for the info...if I can't get a fix from Lowrance I might think about getting the GMI-10. It'll be handy to have the display anyway.

[CarinaPDX]

Whoa there - before we have a lynching, let's back up and think about this a bit. The Lowrance display is recognizing the Garmin-branded Airmar tri-ducer, and is even displaying the readings if I understand correctly. It also is capable of offsetting the depth readings. The only thing it doesn't do is correct the speed readings. This doesn't sound like a nefarious attempt to not work with a competitor's product - it looks like a bug. Before making accusations let's give the vendor a chance to fix the problem. MarkSF: No answer yet - is your MFD up-to-date with version 4.0 software?

The calibration of the speed (as for depth) is done exclusively within the MFD. There are no PGNs that the DST800 recognizes that would communicate any calibration data to the sensor. The sensor outputs uncalibrated data and it is up to the MFD to correct it. The correction for speed is usually a simple multiplier. Certainly Lowrance understands this, and I would be shocked if it weren't implemented in this MFD. My guess is that the software assumes that there is only one function to calibrate per device. Whatever it is, it should be easy to fix in an upcoming bug fix release, if it hasn't been done already. I certainly wouldn't be talking about replacing the MFD at this stage.

One of the shortcomings of N2K is that there is no standardized way of updating device firmware. My Furuno MFD receives updates via SD card, and it in turn can update Furuno devices like my Furuno radar scanner. To update my Maretron compass, and to calibrate it, I had to connect it to my computer via 0183, which seems to be a common solution for other devices. Yes, it is a nuisance, but not a deal-breaker for me. More data for the imaginary thread about what could be better with N2K.

Greg

[s/v Jedi]

@Greg,

The Lowrance does not recognize the Airmar/Garmin transducer. It just receives the N2K PGN and decodes that.

ciao!
Nick.

[colemj]

Originally Posted by CarinaPDX

The calibration of the speed (as for depth) is done exclusively within the MFD. There are no PGNs that the DST800 recognizes that would communicate any calibration data to the sensor. The sensor outputs uncalibrated data and it is up to the MFD to correct it.

I thought this also (and it makes sense), but I calibrated our Airmar depth sounder using the Simrad autopilot controller and the calibrated depth shows up in all MFD's and the computer. When I poll the depth sounder via the Maretron network analyzer, it shows the calibration offset as one of its properties. Same thing when polling it using the Actisense analyzer.

I'm led to believe that the Airmar transducers accept and keep an offset locally.

Mark

[MarkSF]

Originally Posted by CarinaPDX

Whoa there - before we have a lynching, let's back up and think about this a bit. The Lowrance display is recognizing the Garmin-branded Airmar tri-ducer, and is even displaying the readings if I understand correctly. It also is capable of offsetting the depth readings. The only thing it doesn't do is correct the speed readings. This doesn't sound like a nefarious attempt to not work with a competitor's product - it looks like a bug. Before making accusations let's give the vendor a chance to fix the problem. MarkSF: No answer yet - is your MFD up-to-date with version 4.0 software?

The calibration of the speed (as for depth) is done exclusively within the MFD. There are no PGNs that the DST800 recognizes that would communicate any calibration data to the sensor. The sensor outputs uncalibrated data and it is up to the MFD to correct it. The correction for speed is usually a simple multiplier. Certainly Lowrance understands this, and I would be shocked if it weren't implemented in this MFD. My guess is that the software assumes that there is only one function to calibrate per device. Whatever it is, it should be easy to fix in an upcoming bug fix release, if it hasn't been done already. I certainly wouldn't be talking about replacing the MFD at this stage.

Greg

Yes, it does have the version 4.0 software. I am still waiting for a response from Lowrance support. Even if the answer is that the feature is not available right now, I was not intending to replace the chartplotter (especially now I've invested 2 weekends getting the NMEA 0183 interface from the AIS receiver working) but rather to supplement it with a GMI-10 or similar. Any excuse to buy a new gadget...

You are correct that the chartplotter does display depth, speed, and temp from the sensor, and I have set the depth offset. The depth function works beautifully, way more accurate than the old instrument I had. If only the same could be said for speed.

Note that I looked at the Airmar technical reference and there is a calibration sentence that is accepted by the sensor (output FROM the MFD) that calibrates the speed sensor internally. It even has a piece-wise linear multi-point calibration correction. Whether any device exists that outputs it is another matter.